The present invention relates to a projection screen, and more particularly to an improvement in a transmission type projection screen.
Transmission type projection screens, in which an image is projected from the rear side and the projected image is observed from the front side, have been known in the art. Transmission type projection screens of various configurations have been already proposed. Particularly, for the transmission type screens having been recently used for the color television projectors, it is required to have not only a function essential to the screen to diffuse a light toward the side of an observer, but also a function to correct "color shift" produced resulting from the fact that light rays indicating colors of red (R), green (G) and blue (B) are projected from different positions. In addition, reduction of the external reflection is required for the screen which is used for the color television projectors, because the luminance of the color television projectors is not so high that, in a well-lighted room, the indoor or outdoor light is reflected on the screen surface so as to lower the contrast of the projected image, thus to damage visual recognizability.
For the article to satisfy the above-requirement, there is known a lenticular sheet with black stripes comprising a large number of lenticules arranged in a vertical direction on both the surfaces of the sheet, and light absorption layers provided at portions from which light is not emitted of light emission surfaces which will be simply referred to as "emission surfaces" hereinafter.
However, the drawback with the above-mentioned lenticular sheet is that an angle of view of visual field in a horizontal direction is limited to a range of 30 degrees in each of clockwise and counterclockwise directions with the optical axis being as the center, i.e., a narrow range of 60 degrees in total. On the other hand, in order to widen the horizontal viewing angle, there is also known a transmission type screen having a portion where a part of the incident light is totally reflected. However, since an element for correcting color shift is not included in the screen of this type, color shift becomes large. In addition, it is required for reducing the reflection of an external light to provide light absorption layers on the surface from which light is not emitted of the emission surface. Since, in the case of this type of screen, the surface from which light is not emitted is the one on which a part of incident light is totally reflected, it is necessary to provide light absorption layers on the total reflection surface. To realize this, it is required to first provide reflection layers on a surface which is to serve as a total reflection surface and to second provide light absorption layers thereon. In addition, since the surface from which light is not emitted generally exists on a concave portion, it is very difficult to provide respective layers on such a concave portion.